Coagulation test, which is one type of blood test, is conducted by measuring clotting time of blood in order to grasp the state of hemostasis mechanism. When prolongation of clotting time is observed, congenital coagulation disorder due to congenital deficiency or abnormality in blood coagulation factors, or acquired coagulation inhibition due to autoantibodies that inhibit coagulation reaction is suspected as the cause of the prolongation. Congenital coagulation disorder can be distinguished from acquired coagulation inhibition on the basis of a test (cross-mixing test) that measures clotting time of a specimen prepared by mixing a normal plasma and a subject plasma that shows prolongation of clotting time. That is, in the case of congenital coagulation disorder, prolongation of clotting time is corrected by the subject plasma being mixed with the normal plasma, but in the case of acquired coagulation disorder, prolongation of clotting time is not corrected.
In a cross-mixing test, clotting times of a specimen that has just been prepared and a specimen incubated at 37° C. for 2 hours are respectively measured, and on the basis of change in the pattern of a graph on which the obtained clotting times of the respective specimens and mixing ratios of the normal plasma and the subject plasma are plotted, a sample that contains coagulation factor inhibitors or lupus anticoagulant (LA) which are autoantibodies is distinguished from a sample derived from a coagulation factor deficient patient. However, making such distinction by finding the difference in pattern change on the graph requires experience, and there are many cases where only experts can see such difference.
In recent years, for assessment of the entire process from the start of clotting to formation of fibrin clots, analysis of clot waveform has been attracting attention. The clot waveform is a waveform that represents temporal change in optical characteristics such as transmission and scatter of light in the blood sample, the change occurring in accordance with advancement of blood sample clotting. Through the analysis of the clot waveform, information such as velocity and acceleration of coagulation is obtained. For example, U.S. Patent Application Publication No. 2003/0104493 indicates that patients having antiphospholipid antibodies (including IA) and receiving warfarin show maximum coagulation acceleration and maximum coagulation deceleration that are different from those of healthy individuals.
As described above, a coagulation-factor-deficient sample can be distinguished from a blood sample containing coagulation factor inhibitors or LA through a cross-mixing test, which is, however, not quantitative assessment. Further, the cross-mixing test requires a plurality of measurement specimens prepared by mixing a subject plasma and a normal plasma at various ratios, and thus, when the amount of the subject plasma is small, the cross-mixing test cannot be conducted. Therefore, there is a demand for measures that can quantitatively determine whether the blood sample is suspected to be a coagulation-factor-deficient sample, on the basis of measurement data from one measurement specimen.